Medical personnel practicing in the field of neurosurgery have been aware for a number of years of the importance of penetrating a patient's cranium with surgical tools and instruments at an angle of substantially 90.degree.. The purpose behind this practice is twofold: first, a burr hole drilled at an orientation of 90.degree. to the surface of the skull prevents injury to the underlying dura and brain tissue which may otherwise be caused by the continued rotation of the metal bit of the drilling apparatus once the bit tip exits the bone.
That is to say that, when directed into the skull at an orientation of other than 90.degree., the bit of drilling devices in current use often continues to rotate after the tip portion has pierced the cranium, despite the incorporation of a standard safety clutch mechanism commonly utilized with such drills. The operation of this standard clutch is such that the drill should automatically stop rotating once the pressure upon the tip is released, i.e., once the tip of the bit passes entirely through the skull bone.
The drill bit commonly utilized in neurological surgical procedures, however, comprises a fixed outer sleeve and a slidable inner sleeve, partially rotatable within the outer sleeve. This inner sleeve extends a short distance beyond the outer sleeve. If the burr hole is oriented at some angle other than 90.degree., while the trailing edges upon the outer sleeve of the bit are still engaging the bony surface of the patient's skull, the grinding surfaces upon the inner sleeve, which extend beyond those of the outer sleeve as noted above, are quite likely to cause serious injury to the underlying tissue within the cranial cavity.
In contrast, however, a burr hole aligned at an angle of substantially 90.degree. to the surface of the skull permits the clutch mechanism to operate properly and thus stops the rotation of the entire bit once the tip has penetrated the bone, preventing accidental injury to the brain and related tissues within the cranial cavity.
The second and no less important reason for orienting an aperture into the cranial cavity at an angle of substantially 90.degree. to the surface of the skull is to ensure that a surgical tool or instrument which is passed through the aperture and into the underlying tissue of the patient's brain does not deviate from its intended path due to a misaligned skull hole. This feature is particularly important to the success of a number of neurological surgical procedures which include, but which are not limited to such techniques as:
neuroendoscopy; PA1 brain biopsy or stereotactic brain biopsy; PA1 catherization; PA1 placement of brain transplant tissue; PA1 placement of transducers for brain function monitoring; and PA1 the installation of pharmaceuticals within the brain
An apparatus and method for ensuring correct placement of, for example, a catheter, within the patient's cranium, has been disclosed and claimed by one of the present applicants in U.S. Pat. No. 4,613,324 issued Sept. 23, 1986. This apparatus, when positioned over an orifice (previously drilled by other means) above the anterior horn of the lateral ventricle of the brain, guides a catheter with its attendant obdurator through the orifice and into the lateral ventricle at an angle normal to a plane formed by a tangent to the cranium at the orifice.
The device comprises a tubular member which is adapted to receive and guide the catheter through the burr hole in the patient's cranium, having a support which is adapted to rest unsecured upon the cranium in surrounding spaced relation to the orifice. The support and the tubular member are spatially related so as to guide the catheter through the orifice in a direction perpendicular to an imaginary plane defined by a tangent to the cranium at the orifice. The tubular member thus serves to guide the remainder of the catheter when the free end thereof is inserted into the patient's brain.
There is, however, no prior art of which applicants are aware that discloses any apparatus or device capable of properly orienting all of the various surgical and observational instruments which are utilized in the various neurological procedures outlined above. The need for such a device has thus led to a search for an easily assembled working platform which facilitates access to a particular location within the brain of a patient without the occurrence of what may now be characterized as unnecessary trauma to the surrounding tissue.